The invention relates generally to dampers for minimizing vibration associated with impulse speed variation of rotating shafts and, more specifically, dampers for camshafts of internal combustion engines.
The development of smaller displacement, lighter internal combustion engines which typically operate at higher speeds than previous designs has produced engines which, while far more efficient, tend to run less quietly and smoothly than their predecessors. The heavy cast iron block of many prior internal combustion engines inherently functioned as an inertial damper due to its relatively large mass. Vehicle weight reduction campaigns have not overlooked this mass as a target for weight saving and not only less material but also lighter material such as aluminum now frequently comprises the engine block.
A complicating factor of vibration control is the wide R.P.M. range of modern engines which may vary from 800 R.P.M. at idle to 8000 R.P.M. at redline. Such wide operating ranges render vibration control increasingly difficult as a solution effective at 1500 R.P.M. may exacerbate vibration at 3000 or 6000 R.P.M. The problem is also particularly acute with engines having four cylinders but typically reduces in magnitude as the number of cylinders increases.
Accordingly, and especially with regard to four cylinder engines, significant attention has been paid to rotational perturbations of the crankshaft resulting from combustion within the cylinders and piston acceleration and deceleration. Many ancillary devices have been incorporated into internal combustion engines to compensate for these perturbations and provide smoother operation. Internally, these devices take the form of counter- rotating balance shafts, Lanchester dampers and harmonic balancers. Externally, fluid engine mounts and engine mounts having adjustable damping characteristics have been utilized.
For example, U.S. Pat. Nos. 4,683,849 and 4,712,436 teach crankshaft balancing devices wherein weights are disposed on counter-rotating shafts. U.S. Pat. No. 4,688,528 teaches an internal combustion engine wherein reciprocating balance weights are disposed for translation between two rotating cams which are driven by either the crankshaft or cam shaft. U.S. Pat. No. 4,677,948 discloses an engine balancing device comprising a pair of counter-rotating shafts disposed parallel to and below the engine crankshaft. Earlier internal combustion engine crankshaft balancing schemes are disclosed in U.S. Pat. Nos. 2,235,160 and 3,468,190.
U.S. Pat. No. 4,781,156 discloses an engine crankshaft balancer which incorporates a balancing mass suspended from the crankshaft main bearing caps on rods or bolts. U.S. Pat. No. 4,926,810 discloses a generally similar balancing construction. U.S. Pat. No. 5,083,535 teaches a compensating device for use in five cylinder in-line engines including pairs of counter-rotating balance wheels driven by the crankshaft.
The foregoing patents reveal that significant attention has been paid to canceling unwanted vibratory motion and providing improved overall operating balance of internal combustion engines but that the crankshaft has been the prime focus of such attention.
Believing that significant room for improvement exists, further examination of the sources of unwanted vibration in internal combustion engines has been undertaken by the inventors. Such examination has focused on the vibratory characteristics of the camshafts and on means and methods of minimizing and eliminating such vibrations. The present invention is directed to a device which reduces vibration generated by camshafts which result from the intermittent positive and negative torques associated with the opening and closing of valves and thus is capable of improving the operating smoothness of an internal combustion engine.